Old tests were rather weak so we have removed them and made new test set. Now the 1st test is a test from problem statement. All submits were rejudged, about 75% AC submits got WA and TL. Thanks to Vedernikoff Sergey for help.

1. As I've understood, my old solution don't pass new tests only because there are pairs <a, n> : a >= n.

2. Brute force still gets AC in ~0.6 sec.

I can say more: brute works near 0.35 seconds, my earlier solution gets TL because I love symbol "%" very much :D